CZTS

CZTS refers to copper zinc tin sulfide, Cu2ZnSnS4, a quaternary chalcogenide semiconductor used primarily as an absorber layer in thin-film solar cells. It adopts a tetragonal kesterite crystal structure related to the stannite family, and its lattice can exhibit cation disorder among Cu, Zn, and Sn, which influences electronic properties. The material is composed of earth-abundant elements and is considered relatively non-toxic compared with some other PV materials.

The bandgap of CZTS in the sulfide form is around 1.5 eV, making it suitable for single-j-junction photovoltaic devices. The bandgap can be adjusted by substituting sulfur with selenium, producing CZTSSe and enabling a tunable range typically spanning from about 1.0 to 1.5 eV. This tunability supports device optimization for different spectra and device architectures. Typical CZTS solar cells use the absorber layer with a cadmium sulfide (CdS) or alternative buffer layer, followed by a transparent conducting oxide contact and metal electrodes. Processing methods for CZTS include physical vapor deposition techniques such as co-evaporation and sputtering, as well as solution-based approaches and nanoparticle inks.

Despite steady progress, CZTS-based devices face challenges that limit efficiency. Defect chemistry and disorder, particularly Cu/Zn antisite defects and tin-related defects, create deep states and band-tail effects that contribute to voltage losses. Phase stability and quality of interfaces also impact performance. Research focuses on defect engineering, composition optimization (including Zn/Cu ordering and Sn-related defects), improved buffer layers, and post-deposition treatments to enhance crystal quality and reduce recombination losses. CZTS remains attractive for its earth-abundant, potentially Cd-free, thin-film PV applications, with ongoing work aimed at closing the performance gap with CIGS and other technologies.